Unexpected

The mind is drawn to surprises (in the language of Kahneman [Kahneman2011], a core function for System 1 is finding deviations from a norm and highlight a surprise).

The aha-effect or wow-effect is therefore very important.

What about the content is surprising? Counter-intuitive? Beyond the user's expectation?

Concrete

Some parts of the mind are very well adjusted to concrete language (Kahneman would say System 1 has its difficulties in dealing with abstract terms [Kahneman2011]).

In fact, dealing with abstract terms costs mental effort (and leads to ego depletions because of the necessary activation of System 2 [Kahneman2011])

Language of the senses (things we see, things we hear, things we can touch,...) works best. In fact, Feynman uses a language rich in sensory inputs, one can vividly imagine, visualize, the scenes (cf. Notes on Feynman's Lectures)

Language understandable by an 8-year old child, without clutter of technical terms. If Feynman manages that for Quantum Physics, then we should be able to do that for any topic.

Actors interacting or doing something is easier to understand than abstract concepts.

Credible

Internal credibility: richness in details and vivid description.

External credibility: by authority.

Kahneman has something to say about this, because clarity, understandability, readability, etc. spawn a sense of credibility. [Kahneman2011]

Emotional

Emotions are markers for the memory system. That means memories that solicit an emotion are remembered better.